Mechanisms of microbiome-driven cardiac allograft outcomes

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PROJECT SUMMARY Though the one-year survival rate in cardiac transplantation has reached 90-95%, the mortality rate beyond the first year has not changed in the last two decades. Immune-mediated damage remains the primary cause of long-term graft failure. Findings from our and other studies provide the rationale for investigating the gut microbiome as a determinant of post-transplantation outcomes and as a potential tool to induce immune modulation to improve long-term graft outcomes. The goal of this study is to determine the mechanisms by which the gut microbiome impacts allograft outcome. We postulate that the disrupted metabolic activities of the gut microbiome lead to inflammatory responses and intestinal injury via cell-type specific responses in the intestinal cells network, which subsequently modulate alloimmunity and ultimately chronic cardiac graft outcomes. We will take advantage of our clinically-relevant cardiac transplant murine model of chronic rejection with well-characterized alloresponses, induced by pro- or anti-inflammatory bacteria, to determine the alterations in the microbial metabolic activities in Aim 1, then to identify local intestinal barrier changes and the underlying intestinal cell-type specific responses in Aim 2, and finally to characterize systemic alloresponses and graft survival in Aim 3, in order to obtain a holistic understanding of the precise mechanisms of microbiome-driven chronic graft outcomes. The proposed work will identify novel and critical microbiome-based targets for diagnostic application and therapeutic intervention, and discern the complex and bidirectional dialogue between the microbiome and alloimmunity to promote transplant immunologic quiescence and long- term cardiac graft survival.